Field of the Invention
The present disclosure relates to a flexible flat panel display. Especially, the present disclosure relates to a flexible organic light emitting diode display having edge bending structure.
Discussion of the Related Art
Nowadays, various flat panel display devices are developed for overcoming many drawbacks of the cathode ray tube such as heavy weight and bulk volume. The flat panel display devices include the liquid crystal display device (or LCD), the field emission display (or FED), the plasma display panel (or PDP) and the electroluminescence device (or EL).
FIG. 1 is a plane view illustrating the structure of the organic light emitting diode display having the active switching elements such as the thin film transistors according to the related art. FIG. 2 is a cross sectional view illustrating the structure of the organic light emitting diode display along to the cutting line of I-I′ in FIG. 1 according to the related art.
Referring to FIGS. 1 and 2, the organic light emitting diode display comprises a thin film transistor (or ‘TFT’) substrate having the thin film transistors ST and DT and an organic light emitting diode OLE connected to and driven by the thin film transistors ST and DT, and a barrier film BF joining and facing the thin film transistor substrate with a sealant SE therebetween. The thin film transistor substrate includes a switching thin film transistor ST, a driving thin film transistor DT connected to the switching thin film transistor ST, and an organic light emitting diode OLE connected to the driving thin film transistor DT.
On a transparent substrate SUB, the switching thin film transistor ST is formed where a gate line GL and a data line DL are crossing each other. The switching thin film transistor ST acts for selecting the pixel which is connected to the switching thin film transistor ST. The switching thin film transistor ST includes a gate electrode SG branching from the gate line GL, a semiconductor channel layer SA overlapping with the gate electrode SG, a source electrode SS and a drain electrode SD. The driving thin film transistor DT acts for driving an anode electrode ANO of the organic light emitting diode OD disposed at the pixel selected by the switching thin film transistor ST. The driving thin film transistor DT includes a gate electrode DG connected to the drain electrode SD of the switching thin film transistor ST, a semiconductor channel layer DA, a source electrode DS connected to the driving current line VDD, and a drain electrode DD. The drain electrode DD of the driving thin film transistor DT is connected to the anode electrode ANO of the organic light emitting diode OLE.
As one example, FIG. 2 shows the thin film transistor of top gate structure. In this case, the semiconductor channel layers SA and DA of the switching thin film transistor ST and the driving thin film transistor DT are firstly formed on the substrate SUB and the gate insulating layer GI covers them and then the gate electrodes SG and DG are formed thereon by overlapping with the center portion of the semiconductor channel layers SA and DA. After that, at both sides of the semiconductor channel layers SA and DA, the source electrodes SS and DS and the drain electrodes SD and DD are connected thereto through contact holes penetrating an insulating layer IN. The source electrodes SS and DS and the drain electrodes SD and DD are formed on the insulating layer IN.
In addition, at the outer area of the substrate SUB surrounding the display area where the pixel area is disposed, a gate pad GP formed at one end of the gate line GL, a data pad DP formed at one end of the data line DL, and a driving current pad VDP formed at one end of the driving current line VDD are arrayed. As the gate pad GP is disposed at the different layer from the data pad DP, some defects may occur at the overlapping portion due to the level difference.
A passivation layer PAS is disposed to cover the upper entire surface of the substrate SUB having the switching and the driving thin film transistors ST and DT. After that, formed are the contact holes exposing the gate pad GP, the data pad DP, the driving current pad VDP and the drain electrode DD of the driving thin film transistor DD. Over the display area within the substrate SUB, a planar layer PL is coated. Patterning the planar layer PL, a contact hole is formed for exposing the drain electrode DD of the driving thin film transistor DT. Further, the planar layer PL is patterned as exposing the full areas of the pads at gate pad GP and the data pad DP. The planar layer PL makes the roughness of the upper surface of the substrate SUB in much smoother condition, for coating the organic materials composing the organic light emitting diode on the smooth and planar surface condition of the substrate SUB.
On the planar layer PL, the anode electrode ANO is formed to connect the drain electrode DD of the driving thin film transistor DT through one of the contact holes. On the other hands, at the outer area of the display area not having the planar layer PL, formed are a gate pad electrode GPT, a data pad electrode DPT and a driving current electrode VDPT connected to the gate pad GP, the data pad DP and the driving current pad VDP, respectively, exposed through the contact holes. On the substrate SUB, a bank BN is formed covering the display area, excepting the pixel area.
After completing the thin film transistor substrate, an inorganic material such as the silicon nitride (SiNx) is deposited over the entire surface of the substrate SUB with a thickness of 1˜3 μm for preventing the organic light emitting diode from the invasion of the moisture or oxygen gas. Further, a sealant SE is disposed on the inner surface of the barrier film. It is preferable that the sealant SE has the boundary being apart with a predetermined distance from the edges of the barrier plate BF to the inside.
Aligning the barrier plate BF on the thin film transistor substrate, the barrier plate BF is attached/joined with the thin film transistor substrate under pressure. After hardening the sealant SE between the barrier film and the thin film transistor substrate, and then releasing the pressure, the thin film transistor substrate has the surface sealing structure by the barrier plate BF with the sealant SE. It is preferable that the barrier plate BF is a film including plastic or organic material.
It is preferable that the sealant SE and the barrier plate BF covers most of all surface of the thin film substrate without the pad area because the pads would be connected to exterior devices. As exposed at outside, the gate pad GP, the gate pad terminal GPT, the data pad GP and the data pad terminal DPT would be connected to the exterior devices through a connecting means.
According to the relative art, the organic light emitting diode display is formed on a rigid substrate SUB. AS the substrate SUB having the rigid property, it is proper to apply for the monitor, television set or portable display module. However, in the market, more various types of the display are required.
For example, the needs for the flexible display freely bendable or foldable are increasing. Further, the needs for the non-bezel or the narrow bezel display are also increasing, by bending or folding the non display area (on which the display information is not shown) over the lateral sides or rear side. In order to develop these various style displays, it is required that the flexible display that the display elements is formed on the flexible substrate.